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What To Know About SMA Prenatal Testing and Diagnosis

Medically reviewed by Evelyn O. Berman, M.D.
Written by Eli Sachse, RN
Updated on June 15, 2023

If you’re an expecting parent with a family history of spinal muscular atrophy (SMA), you may have been advised to consider prenatal genetic testing for your baby. There are many important considerations and decisions to make regarding genetic testing, and each family’s situation is unique.

Understanding the reasons and risks behind prenatal genetic testing can help you be well informed and prepared to make the best decisions for your family.

Who Should Consider Genetic Testing?

SMA is an autosomal recessive condition. That means it is a genetic disorder that can be passed from parents to their children. However, the parents don’t necessarily need to have the condition themselves to pass it on. Parents who aren’t affected by a genetic condition they pass on are called carriers.

If you have family members with SMA or known carriers in your family, you may be referred to genetic counseling for advice regarding genetic testing. Genetic testing for potential carriers of SMA can be done by a simple blood test. A genetic counselor can discuss the likelihood of potential parents passing on SMA to their children.

Carrier testing is not 100 percent accurate in predicting if potential parents will pass on the genes that cause SMA. However, depending on the results of your carrier screening, your genetic counselor will be able to give you probabilities about potentially passing on the condition and provide advice and options.

If both parents test positive for the gene that causes SMA and one is already pregnant, they may be advised to undergo genetic prenatal testing of their baby.

Types of Genetic Prenatal Testing

The two main types of prenatal screening for SMA are amniocentesis and chorionic villus sampling (CVS).

Chorionic Villus Sampling

CVS can be done after the 10th week of pregnancy, so it may be the first choice for those who want a diagnosis as soon as possible. CVS can be performed like a Pap test, through the cervix, or by inserting a needle directly through the abdomen. CVS takes a sample of cells from a specific part of the placenta. The child’s DNA can then be extracted from this sample and tested for the genes that cause SMA.

Amniocentesis

Amniocentesis is performed by extracting amniotic fluid (the fluid surrounding the baby) with a needle inserted directly through the abdomen. It can be performed 15 weeks or later into a pregnancy. The needle is not meant to touch the baby, but there is a risk of infection as well as miscarriage associated with the procedure. DNA from the baby is then extracted from this fluid for testing.

Risks of Prenatal Testing

Both of these kinds of diagnostic testing have a risk of miscarriage. For amniocentesis, the risk is about 1 in 200. For CVS, the risk is about 1 in 100. For any type of invasive procedure (one that breaks the skin), there is the possibility of infection or poor wound healing. Your health care team will take into consideration your health profile in helping you decide whether genetic prenatal testing is the right choice for you.

There’s no right answer in deciding whether to get you or your baby tested. Families can choose or decline testing for personal, cultural, or religious reasons.

Newborn Screening for Spinal Muscular Atrophy

In most states, SMA testing is part of standard newborn screening panels for health conditions. Whether or not you undertake prenatal testing, your baby may be screened for SMA shortly after birth, depending on where you are.

Next Steps and Support

Families whose unborn baby has tested positive for SMA have a lot to learn and carefully consider. Keep in mind that there are several types of SMA, with varying degrees of severity. Life expectancy can range from a few years to a normal life span. SMA treatments have been available for only a few years, so it’s unknown how much they may reduce the severity of symptoms in the long term or extend life expectancy.

Read more about how SMA gene therapy works.

The degree of disability also varies: For some people, SMA is severe and starts early in life; for others, it’s mild and develops later on. Unfortunately, the type of SMA a child will develop cannot yet be diagnosed prenatally.

Decisions around family planning are intensely personal. Some families may choose to terminate a pregnancy and consider starting or growing their family with different fertility options or adoption.

Families choosing to continue the pregnancy should reach out to their primary care provider and OB-GYN to make sure they’ve been informed of the test results. Because SMA is very rare, your health care team may need to educate themselves about the condition and be prepared to provide support.

Several national organizations can provide support in a variety of ways, including:

Read more about parenting a child with SMA.

Talk With Others Who Understand

On mySMAteam, the social network for people with spinal muscular atrophy and their loved ones, more than 2,000 members come together to ask questions, give advice, and share their stories with others who understand life with SMA.

Have you chosen prenatal genetic testing for your family? Share your experience in the comments below, or start a conversation by posting on your Activities page.

Updated on June 15, 2023
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Evelyn O. Berman, M.D. is a neurology and pediatric specialist and treats disorders of the brain in children. Review provided by VeriMed Healthcare Network. Learn more about her here.
Eli Sachse, RN is a registered nurse living in California. He has written about health topics for Sonoma Medicine and Microcosm Publishing. Learn more about him here.

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